This invention relates in general to vehicular braking systems and, in particular, to hydraulic braking systems having pump-operated pressurizing systems.
Hydraulic braking systems, particularly for vehicular applications, can be equipped with pump and controller systems that dynamically vary the fluid pressure in response to sensor inputs. These sensor inputs provide information relating to the dynamic operating state of the vehicle, i.e., skidding conditions, tractive effort conditions, and steering reactions, to name a few. These braking systems, sometimes referred to as antilock braking systems (ABS), traction control systems (TCS), and electro-hydraulic braking systems (EHB), use a motor-driven pump to supply fluid pressure to a wheel-end brake mechanism. The fluid pressure is modulated by a valve circuit to provide proper distribution of braking effort to each wheel in response to a particular vehicle dynamic state.
The hydraulic pumps used to generate hydraulic pressure may be piston-type hydraulic pumps that supply fluid pressure by means of a piston that axially reciprocates within a cylinder bore. These piston pumps generally include a plurality of components, such as pistons, cylinders, bushings, springs, filters, and seals, for example, that are assembled into a pump housing. Because of the generally high fluid pressure levels and the high pressure modulation speeds needed to support antilock braking systems, these hydraulic pumps are precision assemblies requiring that tight machining and assembly tolerances be maintained. Additionally, the design of high pressure sealing systems, which includes material selection and dimensional tolerancing, needs to accommodate both the high fluid pressures and piston reaction speeds without leaking or excessive wearing. Thus, it would be desirable to provide a brake system hydraulic pump that is easier to manufacture and improves fluid pumping performance.